This invention relates to an oil supply system incorporated with a lubricating oil tank pressurized in communication with the crank case through a pressurizing passage and an oil supply passage communicating the aforesaid lubricating oil tank and an oil supply unit.
In general, in this kind of oil supply system applied to a chain saw, for a short period time after its engine is brought to a standstill, under the pressure prevailing inside the lubricating oil tank, lubricating oil is transported to the oil supply unit of the chain saw and it is allowed to flow to the outside. Consequently, in the past, a breather valve is installed on to the lubricating oil tank in such a way that atmosphere and the lubricating oil tank is made to communicate with the external air through a throttling hole and thus, after the engine is brought to a standstill, the pressure inside the lubricating oil tank is allowed to flow out to the atmosphere through the throttling hole for stopping the lubricating oil supply to the oil supply unit. However, as the sectional area of the aforesaid throttling hole was made fixed and invariable, control of the lubricating oil quantity in accordance with a workpiece to be sawn off was unavailable with the result of deteriorating the working efficiency of the chain saw depending upon the nature of the work.